1. Field of the Invention
The subject invention relates to sockets for soldering to printed circuit boards which can accept a pin grid array (PGA) having a plurality of pins.
2. Description of the Prior Art
U.S. Pat. No. 4,498,725; U.S. Pat. No. 4,648,669; and U.S. Pat. No. 4,679,318 relate generally to sockets for pin grid arrays.
Both U.S. Pat. No. 4,648,668 and U.S. Pat. No. 4,498,723 relate to a pin grid array socket which is generally known as a zero insertion force socket. Each of those patents receive a pin grid array and a mechanism is included with the socket which moves the pin grid array into registration with the socket contacts and into electrical engagement therewith.
U.S. Pat. No. 4,679,318 relates to a socket for a pin grid array which is not zero insertion force and the terminals include opposed contact portions which extend upwardly from a strap or bight portion for receiving a pin downwardly therethrough. A shortcoming of this terminal is that the forces to overcome the spreading of the contact arms to accept the pin, referred to as insertion force, are great due to the dynamics resultantly created by the contact configuration.
With reference to FIG. 1, the terminal of U.S. Pat. No. 4,679,318 is depicted where, the registration of the terminal with respect to the pin is shown, and the pin is shown poised for receipt within the terminal and in initial contact with the contact arms. At the moment of contact between the pin and the contact arms, a resultant force F is imposed on each of the contact arms normal to the point of contact.
Referring now to FIG. 2 shows that the force imposed on the contact arms includes two components, a vertical component F.sub.V and a horizontal component F.sub.H. Given that the contact arms will rotate about the interconnection between the contact arms and the strap at a point such as C, the vertical component F.sub.V will impose a clockwise moment on the contact arms, with respect to point C, and will attempt to pinch the contact arms closed. Admittedly, the horizontal component F.sub.H is larger than the vertical F.sub.V and the resultant moment will be counterclockwise about point C, and will open the contact arms and accept the pin. However, the vertical component of the force is doing negative work by attempting to close the contact arms, therefore, the overall force must be increased to achieve a horizontal force large enough to open the contact arms. As the number of pins on the PGAs increases, so will the total insertion force required to insert the PGAs within their associated sockets, which could resultantly damage the PGAs.
Furthermore, the terminal shown in U.S. Pat. No. 4,679,318 appears to use the strap portion and the side walls for retention of the terminal within the respective apertures, which disallows the expansion of the strap portion.
Furthermore, the terminals in U.S. Pat. No. 4,679,318 appear to be box-shaped and are not capable for use in a high density array.